Wireless signaling system



E. F. w. ALEXANDERSON.

WIRELESS SIGNALING SYSTEM.

APPLICATION FILED JAN. 20, 1917.

Patented Aug. 24, 1920.

Inventor: Ernst F W. .71 Iexanderson,

UNITED STATES PATENT OFFICE.

ERNST F. w. ALEXANDERSON, 0F SCHENECTADY, NEW YORK, ASSIGNOR 'IO GENERAL ELECTRIC COMPANY, AcoRroRATIoN on NEW YORK.

WIRELESS SIGNALING SYSTEM.

Application filed January 20, 1917. Serial No. 143,491.

To all whom it may concern:

Be it known that I, ERNST F. W. ALEX- ANDERSON, a Citizen of the United States, residing at Schenectady, in the county of Schenectady, State of New York, have invented certain new and useful Improvements in Wireless Signaling Systems, of which the following is a specification.

My present invention relates to wireless signaling systems, and more particularly to a so-called duplex system in which means is provided for simultaneously sending and receiving messages at a single station. 1

The object of myinvention is to provide means for neutralizing in the receiving circuit or apparatus the effect of waves which are being transmitted, from the same station.

In carrying my invention into effect I employ separate antennae fortransmitting and receiving purposes.- Both of these antennae may ,be, suspended from, the same towers in whole or in part, or may be located in fairly close proximity to each other upon separate towers. In order to overcome the effect in the receiving apparatus of the waves impressed upon the receiving antennae from the transmitting antenna, ,1 derive by direct connectionto the transmitting antenna, an electromotive force equal in, value and opposite in direction to the potential induced ,upon the receiving antenna from the transmitting antenna and impressflthe desired electromotive force upon the receiving circuit in such a manner-as to neutralize inthe receiving apparatus the effect ofthe induced potential. V

The novel features which I believe to be characteristic of my invention are set forth with particularity. in the appended claims- The invention itself, however, both as to particular embodiments thereof andgits mode of operation, will best be understood by reference to the following description taken in connection with the accompanying drawing in which-Figures 1 and 2;Sh0W two modifications. of-[my invention, and Fig. 3 is a diagram explanatory-of the form shown inFi.2. V

In ig. 1 I have indicated a transmitting antenna 1 supported upon towers 2 and 3. Areceiving antenna 4 which is insulated from the transmitting antenna is supported Specification of Letters Patent.

Patented Aug. 2 1, 1920.

upon towers 3 and 5. The receiving antenna maybe supported upon the towers 2 and 3 or may be supported independently of either of these towers but in close enough proximity to the transmitting antenna so that both antennae may be readily connected to the operating station. The transmitting antenna may be supplied with signaling current from a high frequency alternator 6 coupled thereto by means of the coils 7 and 8. The tuning of this antenna may be accomplished by means of the usual. variable inductance "9. The signaling current may be controlled in any desiredg way for transmitting either telegraphic or telephonic signals. ,In case it is desired to transmit telegraphic signals a key may be inserted in serieswith the alternator and coil 7 as indicated in the drawing. The receiving antenna 4 is connected to earth at 10 through the coil 11 which is coupled to the coil 12 in the receiving circuit of the electron discharge device13 which may serve as an am-. plifier and detector for the signals which it is'desired to receive. The receiving circuit comprisesthe cathode 14 of the device, the grid 15 and a variable condenser 16 for tuning the circuit to the frequency of the waves to be received. The detector circuit of the device comprises the cathode 14, anode 17, a battery 18 for supplying the operating current, and the usual telephone receivers 19, these receivers being shunted by the condenser 20 which serves to bypass the high frequency component of the current flowin in the circuit. While the arrangement hown is a preferred form of receiving device other forms may be employed if desired. v v

IVith the system thus far described, when signals are being transmitted potentials of such magnitude will be induced in the receiving antenna that the received signals will be unintelligible even though the two sets of signals may diiferv considerably in frequency. To overcome this difliculty I provide a shunt connection to the transmitting antenna from the point 21 to earth at 22 through the inductance 23. The inducpressed upon the receiving antenna by means of the connecting wire 25, a variable condenser 26 being included in the circuit for tuning it to the frequency of the transmitting current. The two opposing potentials thus neutralize each other and as a result the receiving apparatus will not be affected by the waves transmitted from antenna 1. If any difficulty is experienced in adjusting the neutralizing circuit in such a way as to entirely overcome the effect of the trans mitted waves a frequency trap consisting of a condenser 27 and inductance 28 may be inserted in the receiving circuit. If this frequency trap is tuned to the frequency of the waves transmitted it will offer a high impedance to waves of that frequency and a much lower impedance to received waves which differ somewhat in frequency from the waves transmitted.

In the form of my invention shown in Fig. 2 the neutralization of the induced potentials in the receiving antenna is accomplished by an arrangement of electrostatic condensers. The neutralization effect in this case is to the highest possible degree independent of the frequency and therefore a higher degree of neutralization is possible. The neutralization is also'independent of fluctuations in the operation of the transmitting apparatus and the regulation of the system is simple. The operation of this system is based upon the Wheatstone bridge principle and will be best understood by reference to the diagram of Fig. 3. diagram the condenser 29 represents the capacity between the receiving aerial and ground. The corresponding-capacity on the other side is the condenser 30 which I ter the counterpoise condenser. This is inserted in the ground connection of the receiving antenna as indicated in Fig. 2. The capacity of the receiving aerial is fixed by the antenna structure and the counterpoise condenser has a fixed capacity which is not changed during the operation of the system. The third arm of the bridge which I term the exposure capacity of the receiving aerial comprises the natural capacity between the transmitting and receiving antennze. and is represented by the condenser 81. This capacity also. is determined by the antenna structure and is substantially constant. To balance this exposure capacity I employ a condenser 32 whichI term the exposure capacity of the counterpoise. The condenser 32 is variable and by adjusting its capacity it is possible to balance the system in such a way that the points 38 and 34 at the ends of'the receiving coilll are at equal potentials in so far as the transmitted waves are concerned. In this arrangement the potential across. the capacity '31 represents the i-nduced potential on the receiving antenna and thewpotential across condenser In this 32 is a potential derived directly from the transmitting antenna which is connected to the receiving coil 11 in such away as to neutralize therein the effect of the potential across capacity 81'. In actual practice it may be convenient to divide condenser 32 into two parts as indicated in Fig. 2 where 35 is a fixed capacity and 36 is a variable condenser by means of which the operator can easily balance the system.

While the potential due to the signal transmission is equal upon the two terminals of coil 11, it will be apparent from a'consideration of Fig. 3 that, both of these terminals have a considerable potential difference above ground.- Some care is therefore necessary in designingthe transformer of which coil 11 is the primary in order that the electrostatic influence between the primary and secondary winding of the trans- V former shall be well neutralized and balanced so that this electrostatic influence will not produce currents in the receiving apparatus. In the present instance, this object is accomplished by constructing the secondary winding of two carefully balanced coils37 and 38 connected in multiple, the middle point of the winding of each of these secondary coils being grounded at 39, as indicated.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. The combination in a wireless signaling system of a receiving antenna, a separate transmitting antenna in' proximity thereto, and a receiving coil having one end connected to said receiving antenna and its opposite end connected toa point between two capacities one of which is connected to earth and the other of which is connected to the transmitting antenna.

2.'The combination in a wireless signaling system of a receiving antenna, a separate transmitting antenna in proximity thereto,

and a receiving coil having one end con.-

nected to said receiving antenna and its opposite end connected to'a point between two capacities, one of which is connected to earth and the other of which is connected to the transmitting antenna,the two capacities being so proportioned with respect to the capacity of the receivingantenna and the mutual capacity between the antennae that the two ends of the coil are at equal potentials with respect to the transmitted waves. r r

3. The'combination in'a wireless signaling system of a receiving'antenna, a separate transmitting antenna in proximity thereto and a system of condensers connected to the transmitting antenna and so proportioned with respect to the capacity of the receiving antenna and the. mutual capacity between the two antennae that a point betweenadjacent'condensers is at the same potential with respect to the transmitted waves as the receiving antenna.

a. The combination in a wireless signaling system of a receiving antenna, a separate transmitting antenna in proximity thereto, and a receiving coil having one end connected to the receiving antenna and its other end connected to a point which is of equal potential with respect to the transmitted waves.

5. The combination in a wireless signaling system of a receiving antenna, a sepa rate transmitting antenna in proximity thereto and a receiving coil, the two ends of which are connected to points which are at equal potentials with respect to the transmitted waves.

6. The combination in a wireless signaling system of a receiving antenna, a separate transmitting antenna in proximity thereto, and a system of condensers directly connected to the transmitting antenna and so proportioned that a point between two of said condensers will be at the same potential with respect to the transmitted waves as the receiving antenna.

7. The combination in a wireless signaling system of a receiving antenna, a separate transmitting antenna in proximity thereto, a system of condensers connected to the transmitting antenna for obtaining a point which is at the same time potential with respect to the transmitted waves as the receiving antenna and receiving apparatus connected between the receiving antenna and the equi-potential point thus obtained.

8. The combination in a wireless signaling system of a receiving antenna, a separate transmitting antenna in proximity thereto, a connection to the transmitting antenna for obtaining a point which is at the same potential with respect to the transmitted waves as the receiving antenna and receiving apparatus connected between the receiving a11- tenna and the point thus obtained.

In witness whereof I have hereunto set my hand this 19th day of January, 1917.

ERNST F. WV. ALEAAN DERS ON. 

